Effect of sodium valproate on hypothalamic neurons in vivo and in vitro.

The effects of sodium valproate on extracellularly recorded spontaneous neuronal activity and its interaction with GABA-induced inhibition were assessed in the rat medial basal hypothalamus both in situ and in explant culture. In situ, valproate enhanced the spontaneous rate in 14 of 20 neurons sampled, 6 neurons were unaffected. In vitro, valproate had an inconsistent effect on firing rate; the spontaneous rate was decreased in 6 cells, elevated in 1, while 17 either were unchanged or demonstrated no consistent pattern of response. Both in vivo and in vitro, valproate produced a variable effect on GABA induced inhibition. In vivo, the modal response of valproate on GABA inhibition was antagonism whereas the response in vitro was less consistent, favoring no change in GABA inhibition. The results of this study suggest that valproate exerts an inconsistent action on hypothalamic neurons. These findings are in contrast to those from the cerebral cortex, suggesting that the action of valproate in the brain may be regionally specific.